1. Field of the Invention
The present invention relates to medical diagnostic and screening apparatus and methods. Particularly, the present invention relates to non-invasive medical diagnostic and screening systems. Still more particularly, the present invention relates to non-invasive imaging and functional analysis systems for evaluating cardiac and cardiovascular health.
2. Related Art
Cardiac imaging and functional analysis is the largest single nuclear medical imaging application and represents the area of greatest unmet need in the prior art. This need is exemplified by the fact that historically, for 30%-50% of those stricken with coronary occlusive (artery) disease, the first symptom of the disease is death. This outcome has motivated considerable interest in developing diagnostic methods and apparatus to detect the condition of coronary occlusive disease prior to the onset of fatal symptoms, and further to assist in the development and implementation of preventive measures.
First-Pass RNA
First-Pass Radionucleide Angiography (RNA) provides the clinician with patient information for improved patient management that is either difficult and/or costly to obtain using other technologies. The First-Pass RNA can provide unique qualitative and quantitative information about cardiac function such as regional ventricular wall motion just at the peak of maximum exercise stress, left and right ventricular ejection fraction, regional contractivity, and left to right shunt quantitation. Concurrently, improvements in software analysis of the diagnostic tests are being developed and implemented on a regular basis. However, medical instrument improvements have not kept pace with detector hardware enhancements such as pixellated scintillation crystals, and position-sensitive photomultipliers. Presently, the nuclear medicine health care sector can perform a firstxe2x80x94pass RNA diagnostic protocol using the commercially available dedicated cardiac imager multicrystal scanner model SIM400 from Picker International or a single crystal Anger gamma camera. The single crystal Anger camera has numerous disadvantages when used for first-pass RNA related to its low count rate capability including pulse-pileup and low count density. A low-count density image limits the ability to define changes in wall motion. Improvements in defining wall motion are attained using the multicrystal high rate camera. Other factors influencing the image quality are the intrinsic system resolution, count density, and the target-to-nontarget ratio.
The SIM400 scanner uses a 2.54 cm thick Na1(TI) crystal divided into 400 detector elements in a 20xc3x9720 matrix. Surrounding each detector element is reflective material. Every second row is partially cut through the crystal to create a scintillation bridge between two adjacent elements. The scintillation light is detected by 115xc2xexe2x80x3 diameter bialkali tubes and each photomultiplier tube (PMT) detects scintillation from two optically decoupled detector elements. Variations in pulse output from adjacent PMTs viewing the doublet detector element provides the photon spatial information. This scenario provides for improved count rate capability but limits spatial resolution. 
In practice, clinical interpretations of the SIM400 scanner treadmill stress acquisitions are more difficult to analyze. Patient motion during peak stress acquisition can cause image artifacts that can trigger an incorrect diagnosis. To counteract this problem Picker International uses an Am-241 source placed on the patients"" chest. Dual energy windows are utilized during treadmill stress acquisitions and the Am-241 energy window is used to correct for patient motion. Unfortunately, this method only corrects for up/down/side planar motion, i.e., motion in a plane, and motion in any direction outside the defined plane is uncorrected. If the patient rotates along the z-axis, the planar patient correction can magnify image artifacts. The solution of using an array of fast compact photomultiplier tubes (PMTs) to obtain compact application-specific highrate gamma cameras is described in literature. However, the prior art instruments were slow, designed primarily for relatively low rate (up to 5 kHz) breast imagers. The array concept was conceived and first tested in a small laboratory prototype by Dr. Roberto Pani and his group in University xe2x80x9cLa Sapienzaxe2x80x9d in Rome, Italy. At the time of this application, there are three companies in US that are developing products based on this mature and reliable concept: Gamma Medica Instruments (www.gammamedica.com), Dilon Technologies (www.dilon.com), and PEM Technologies, Bethesda, Md. Initially, imaging of breast cancers was emphasized, taking advantage of the small size of the cameras that allows flexibility in positioning the detector for better localization and visualization of breast lesions. One company, Digirad (www.digirad.com), produces heart imagers based on not yet technically mature and expensive solid state technology (CsI(T1) scintillator and PIN diode arrays). The only high count-rate dedicated heart imager (developed by Proportional Technologies, Inc. Houston) is based on a high pressure wire chamber concept and therefore has its energy range practically limited to less than 100 keV. Also, its rate capability is in fact limited by the physical nature of radiation interaction with a gas detector medium in a two-step process.
Positron Imaging
At the present time, essentially all nuclear cardiac imaging is limited to single-photon tomography for myocardial perfusion determination. This examination is more accurately performed by positron imaging. Prior to cardiac revascularization there is a great need to determine the viability of hypoperfused myocardium. This is accurately determined only by positron imaging. The capability to image the annihilation radiation from positron tracers will greatly increase the usefulness of a cardiac gamma camera. From the list of the presently available detection technologies of: crystal scintillators with photomultipliers, scintillators with PIN photodiodes, scintillators with avalanche photodiodes (APDS), gas filled detectors, Cadmium Zinc Telluride (CdZnTe) and other solid state detection materials, only the first solution is viable at this time from the technical and economical point of view and can be used for positron imaging as well as single gamma imaging. The detection efficiency and excellent signal to noise ratio, good energy resolution, and above all the unmatched speed of operation of fast scintillator/compact photomultiplier combination makes it the solution of choice for a combined single gamma/positron imager. The easily implemented modular structure with segmented fast readout adds to the list of main advantages of this preferred solution. However, it is possible that further development of some of the other detection technologies can lead to another option for the screening and diagnostic instruments and procedures described in this disclosure.
Coronary Artery Disease (CAD) Screening
There are two screening strategies to reduce morbidity and mortality from CAD. The first involves screening for modifiable cardiac risk factors, such as hypertension, elevated serum cholesterol, cigarette smoking, physical inactivity, and diet. The second strategy is early detection of asymptomatic CAD. The principal tests for detecting asymptomatic CAD include resting and exercise ECGs, which can provide evidence of previous silent myocardial infarctions and silent or inducible myocardial ischemia. Another principal test is computed tomography (CT) calcification scoring, which can provide visual evidence of plaques in the coronary arteries. Thallium201 scintigraphy, exercise echocardiography, and ambulatory ECG (Holter monitoring) are less commonly used for screening purposes. Neither of these strategies has produced a solution to the high incidence of previously asymptomatic CAD deaths.
Need for Solutions
In summary, nuclear cardiology equipment has evolved in recent years in the direction of more complex and expensive devices. However, the need for such high-performance imaging technology remains acute. Accordingly, there exists a need for a dedicated nuclear cardiac imaging equipment that is simpler in design, manufacture and use than the prior art. A need also exists for such simple, low cost equipment that can perform first pass imaging, positron imaging, quantitative myocardial perfusion measurements, multi-gated equilibrium pooled blood (MUGA) imaging and coronary transit-time screening. Further, there is a need for portability of such a device.
Naturally, several embodiments of such an invention could solve many or all of the unmet needs of the prior art, and will simultaneously implement new procedures in nuclear medicine that are not currently utilized. Emergency room cardiac triage and bedside patient monitoring are examples of applications that can utilize portable, compact imaging detectors such that the imaging equipment can be taken to the patient vs. the patient taken to the equipment. The portability of the camera also lends itself for imaging in other situations where a patient movement is undesirable. For instance, patients with kidney transplants require frequent evaluation of blood flow and function using renal tracers. Determination of brain viability is also best done at bedside. The risk of transporting these patients to nuclear medicine department inhibits currently optimal utilization of these diagnostic techniques.
Related teachings and prior art include the following:
[1] Dr. Roberto Pani""s papers on multi-PSPMT imagers:
a) Single Photon Emission Imaging by Position Sensitive PMT. Pani R., Pellegrini R., Soluri A., De Vincentis G., Scafxc3xa9 R., Pergola A, Nucl. Instr. and Meth. 1998. A 409:524-528.
b) Multi PSPMT Scintillating camera. Pani R., Soluri A., Scafxc3xa9 R.,Pergola A., Pellegrini R., De Vincentis G.,G. Trotta, Scopinaro F. 1997 IEEE Nuclear Science Simposium, Conference Record vol.2 pg. 1068-1072, Nov. 9-15,1997 Albuquerque, N. Mex. USA.
c) Multi PSPMT Scintillating camera. Pani R., Soluri A., Pergola A., Pellegrini R., Scafxc3xa9 R., De Vincentis G., Scopinaro F. IEEE Trans. on Nuclear Science 46 N.3; 702-708, 1999.
[2] New Developments in Portable Gamma Cameras. Joyce Ward, ADVANCE for Radiologic Science Professionals, page 16-17, Aug. 3, 1998.
[3] U.S. Pat. No. 6,091,070: Semiconductor Gamma-Ray Camera and Medical Imaging System, Lingren C. L. et al., Jul. 18, 2000.
[4] U.S. Pat. No. 4,458,688: Method and Apparatus for Cardiac Nuclear Imaging, Von Behren P. L., Jul. 10, 1984.
[5] U.S. Pat. No. 4,999,501: High speed multiwire photon camera, Lacy J. L., Mar. 12, 1991.
[6] U.S. Pat. No. 5,753,917: Dual crystal scintillation camera, Engdahl J. C. May 19, 1998.
[7] U.S. Pat. No. 5,431,161: Method and apparatus for information acquistion, processing, and display within a medical camera system, Ryals Carl J. et al., Jul. 11, 1995.
[8] U.S. Pat. No. 5,377,681: Method of diagnosing impaired blood flow, Drane Walter E., Jan. 3, 1995.
[9] U.S. Pat. No. 5,249,124: Multi-isotope imaging using energy-weighted acquisition for, e.g., myocardial perfusion studies, DeVito; Raymond P., Sep. 28, 1993.
[10] U.S. Pat. No. 5,199,438: Measurement of cardiac performance, Pearlman Andrew L. Apr. 6, 1993.
[11] Scintillation products from Saint Gobain Crystals and Detectors (formerly: Bicron Corporation), Newbury, Ohio.
[12] Compact and Flat Panel photomulltipliers from Hamamatsu Corporation, Bridgewater, N.J.
[13] Model 85001 000 photomultiplier from Burle Industries, Inc, Lancaster, Pa.
To overcome the above-mentioned shortcomings of the prior art, a dedicated cardiovascular imaging and functional analysis system is disclosed.
The present invention has several unique technical features, including pixellated scintillation detectors, fast compact photomultipliers, matching high efficiency light guide system, very fast readout and data processing systems, and novel imaging and functional analysis algorithms. In a first embodiment of the dedicated cardiovascular imaging and functional analysis system, the cardiovascular imaging system of the present invention comprises a dedicated fast, sensitive, compact and economical imaging gamma camera system that is especially suited for heart imaging. The cardiovascular imaging system of the present invention can be used as a dedicated nuclear cardiology small field of view imaging camera. Embodiments of the present invention for dedicated nuclear cardiographic imaging will compete with magnetic resonance imaging (MRI), computed tomography (CT), and echocardiography; all of which are slowly adopting nuclear cardiology practice. The present invention has the advantages of being able to image physiology, yet also has the potential to be inexpensive and portable, unlike current nuclear medical, MRI, CT, and echocardiography systems.
The cardiovascular imaging system of the present invention employs a basic modular design that can be used in the compact camera system suitable for cardiac imaging with one or more radionucleide tracers. The detector can be positioned in close proximity to the chest and heart from several different projections, making it possible rapidly to accumulate data for first-pass analysis and ejection fraction of both right and left ventricles. The portability of the instrument would also make it very desirable for imaging in the cramped quarters of intensive care units in the cases when it would be not practical to transport the patients to the nuclear cardiology department. Furthermore, preferred embodiments of the present invention include at least a second camera head, routinely placed at approximately a right angle to the first camera head to provide additional out-of-plane views. The additional camera angle permits the system to account for patient motion in all planes, and eliminating artifacts caused by such patient motion. This is especially useful in traditional stress testing.
In a second preferred embodiment, the Cardiovascular Non-Invasive Screening Probe system is to perform a novel diagnostic screening test for potential victims of coronary occlusive disease. This system will provide a rapid, inexpensive preliminary indication of coronary occlusive disease by measuring the activity of emitted particles from an injected bolus of radioactive tracer. Ratios of this activity with the time progression of the injected bolus of radioactive tracer will be used to perform diagnosis of the coronary patency (artery disease).
In this preferred embodiment, this screening test detects coronary insufficiency. Most resting patients with occlusive disease of proximal coronary arteries maintain normal coronary (volume) blood flow. During this period, all standard measures of cardiac hemodynamic functions, i.e., those tests used by today""s cardiologists, are not sensitive to a coronary insufficiency. That is why traditional xe2x80x9cstressxe2x80x9d tests involving periods of increased heart activity are needed to detect coronary disease. A preferred embodiment of the present invention will be able to detect coronary occlusion while patients are resting, and without requiring chemical or other inducement of cardiac stress. In this form, the test is much less stressful and can be performed on patients for whom a standard stress test would be difficult to perform or even dangerous.
Both instruments disclosed in the present submission share the same basic detection technology and have similar basic structure.